Very young childern's comprehension of others' emotional states and their interactions with persons in distress were investigated. Twenty-four mother-child pairs were studied for a 9-month period. The children were 9, 15, or 21 months old at the beginning of the study. Trained mother observers recorded their children's responses to naturally occurring emotions and to simulated distresses. Between 10 months and 2 and one-half years of age there were identifiable developmental transitions in children's responses to witnessed distress in another person. The repertoire of children 10-12 months is limited; mainly signs of general agitation occur in the presence of another person's emotions. The first responses directed toward the distressed person appear between 12 and 15 months; these are primarily positive physical contacts. An expanded range of responses including imitation of victim's emotional expression, self-reference, offering of material and psychological comfort - develops between 18 and 24 months. Individual response patterns to distress are also discernible. Developmental changes are discussed in terms of Hoffman's theory of the development of empathy and altruism.